The present invention relates to improvements in apparatus for feeding sheet material in sheet utilization devices, such as printers and document copiers. The invention addresses the technical problem of loading and unloading sheet cassettes from such devices without having the sheet-feeding mechanism of such devices disturb the alignment and registration of sheets contained by the cassette.
In printers and document copiers, it is common to sequentially feed cut sheets of material (e.g., film or paper) from a sheet supply station to an image recording or transfer station where image information is produced on the individual sheets. In many such devices, the cut sheets are stacked in a sheet supply tray or cassette which can be readily removed from the sheet-feeding station for purposes of reloading the cassette with additional sheets or for substituting a different cassette containing sheets of a different size. Typically, the sheet-feeding stations of the printer or copier includes one or more sheet-picking rollers (e.g., scuff rollers) which, when positioned to engage the topmost sheet in the stack and suitably driven, serve to advance such sheet along a desired sheet path.
Prior to unloading a sheet cassette from a sheet supply station, it is common practice to displace the sheet-feeding roller from the topmost sheet in the stack. Otherwise, frictional engagement between the feed roller and the topmost sheet will act to upset the alignment of the sheets in the stack during removal movement of the cassette from the sheet-feeding station. If unnoticed and uncorrected, such misalignment of the sheets can ultimately produce paper jams, either in the sheet supply station, or further downstream along the sheet-feeding path.
Heretofore, it has been common to use some sort of electromechanical mechanism to achieve the desired spacial relationship between the sheet-feeding roller and the sheet stack prior to unloading the sheet cassette from the printer or copier. Such mechanism usually serves either to lower the sheet stack with respect to the feed roller, or to raise the feed roller with respect to the sheet stack. Electromechanical mechanisms which incorporate solenoids and motors are often used to achieve such lowering or raising functions. Such mechanisms, of course, not only add significant cost to the equipment, but also have an adverse impact on its reliability.